Surfaces with high repellency for water are considered as being superhydrophobic and surfaces with high repellency for oil as being superoleophobic.
Superamphiphobic surfaces are surface having both water and oil repellent behaviour. Such surfaces simultaneously show superhydrophobic and superoleophobic properties.
Numerous studies have shown that some biological species have surfaces with superhydrophobic properties such as for example mosquito's eyes, water strider and lotus leafs.
Attempts have been made to achieve biomimetic materials with superhydrophobic properties, but few of these materials have superoleophobic properties.
Liquid repellent surfaces can be produced by lowering the surface energy of a surface and controlling the roughness of the materials.
Numerous methods have been widely reported in the last decade to process superhydrophobic surfaces by various chemical or physical approaches.
Superhydrophobic surfaces may be prepared from amorphous carbon (a-C) films as described for example by Ying Zhou et al. in Colloids and Surfaces A: Physicochemical and Engineering Aspects volume 335 (2009) pages 128 to 132, from nanotubes as described for example by Sunny Sethi et al. in Langmuir 2009, volume 25(8), pages 4311 to 4313, from Silica particles as described for example by Xing Yi Ling et al. in Langmuir, 2009, volume 25 (5), pages 3260 to 3263, or from ZnO nanorods as described for example by Min Guo et al. in Thin Solid Films, volume 515 (2007) pages 7162 to 7166.
Furthermore, hybrid organic/inorganic composites have also been investigated on the basis of sol-gel-derived titania or alumina/dodecylamine as described in Bai J. Bharathi et al. in Applied Surface Science volume 255 (2009) pages 4479 to 4483, or by embedding hydrophobically modified fumed silica (HMFS) particles in polyvinylidene fluoride (PVDF) matrix as described by V. V. Vinogradov et al. in The Journal of Sol-Gel Science and Technology (2010) volume 53 pages 312 to 315.
Fluorinated functional composites or fluorinated polymers coatings have been deposited on a wide range of custom-made micro/nanostructures using a replication template as described for example by Woo Lee et al. in Langmuir, 2004, volume 20 (18), pages 7665 to 7669.
These studies generally relate to hybrid preparation methods comprising two distinctive steps, such as for example a colloidal lithography as described for example by Yunfeng Li et al. in Langmuir (2010), volume 26 (12), pages 9842 to 9847, followed by initiated chemical vapor deposition as described for example by J. Nathan et al. in Chemistry of Materials 2009, volume 21, pages 742 to 750, or by using silicon nanowires via electroless etching step followed by fluorine carbon coatings as described for example by Beom Seok Kim et al. in Langmuir, volume 27 (16), pages 10148 to 10156.
Another hybrid method has been described by C. Becker et al. in Journal of Physical Chemistry C, 2011, volume 115 (21), pages 10675 to 10681, comprising a laser irradiation and a magnetron deposition of a fluoropolymer thin film.
However, numerous studies have shown difficulties to achieve superhydrophobic coatings by a single step method.
Nanostructured superhydrophobic surfaces have been described by E. Martines et al. in Nano Letters, volume 5 (10) pages 2097 to 2103, by K. Lau et al. in Nano Letters, volume 3 page 1701 (2003) and S. M. M. Ramos et al. in Journal of Applied Physics (2009) volume 106 page 024305.
However, the conditions allegedly required for obtaining such nanostructured surfaces with high contact angle values and low water contact angle hysteresis (WCAH) are very restrictive.
Furthermore, such superhydrophobic surfaces could not be considered as superamphiphobic surfaces as they have only limited superoleophobic properties.
Other attempts were made using SiO2 nanoparticles (Zhoukun He et al. in Soft Matter, 2011, volume 7, pages 6435 to 6443) or carbon nanotubes (Huanjun Li et al. Angewandte Chemie International Edition 2001, volume 40 (9), pages 1743 to 1746) by electrochemistry from metallic samples in perfluorocarboxylate based electrolytes (Haifeng Meng at al. in Journal of Physical Chemistry C, 2008, volume 112 (30), pages 11454 to 11458) or by electrospinning of fluoro compounds fibers (Gyoung-Rin Choi et al. in Macromolecular Materials and Engineering, 2010, volume 295, pages 995 to 1002) or by anisotropic etching of silicon coated with a thin hydrophobic layer (Ramasamy Thangavelu Rajendra Kumar at al. in Journal of Physical Chemistry C, 2010, volume 114 (7), pages 2936 to 2940).
Low surface energy fluorocarbon polymer coatings have been prepared, as disclosed by Virendra Kumar et al. in Plasma Processes and Polymers, 2010, volume 7, pages 926 to 938, via plasma enhanced chemical vapor deposition (PECVD) of 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) in a low pressure inductively excited RF plasma, by initiated chemical vapor deposition as described by Malancha Gupta et al. in Langmuir 2006, volume 22, pages 10047 to 10052, or in corona discharge using 1H,1H,2H,2H-Heptadecafluorodecyl acrylate (HDFDA) as disclosed by P. Anthony et al. in chemistry of materials, 2009, 21, pages 4401 to 4403.
The plasma polymerized PFDA coating thus obtained showed good chemical characteristics, however its water contact angle (WCA) is low, i.e. around 120°. It is assumed that a low roughness achieved by these deposition methods triggers this low WCA.
Furthermore, L. Laguardia et al. in Macromolecular Symposia 2007, volume 247, pages 295 to 302 discloses the deposition of a fluorocarbon film, using 1H, 1H, 2H-perfluoro-1-dodecene as monomer, in a continuous radio frequency (RF) glow discharge. The water- and oil-repellent coating thus obtained has a relatively high contact angle for water of 134° and 116° for di-iodomethane with an average roughness (Ra) of 2.8 nm.
Xuyan Liu et al. discloses in Applied Surface Science, volume 257 (2011), pages 8828 to 8835, the modification of the surface of polyvinylidene fluoride (PVDF) film by a RF atmospheric plasma treatment using argon as carrier gas to obtain a film having amphiphobic properties.
However, none of these coatings combine both superhydrophobic and superoleophobic properties, as such, for example, of having apparent contact angle (CA) above 150° for water and oil.